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Why aren't "fuel polishing" systems removing water & ice from fuel in aircraft, like in cruising yachts?
Should you sump fuel tanks when the fuel system is below freezing? the question

should one sump fuel-tanks before flying, if in freezing-conditions?

but this implies another question that boggles me:
Why don't aircraft have "fuel polishing" systems, to remove water from tanked fuel, especially since the cost of having a line block with ice, is so horribly high?
Cruising boats sometimes have such things, & given the peace-of-mind it'd give, why aren't these devices in play, in aviation??
( btw, it essentially is a filter & water-bypass thingy, so the water goes to the bottom of the glass bowl, & the fuel, above that, goes through the filter, if they combine them, or maybe the water-separator & the filter-unit are separate, in sequence, but both are present, before the fuel goes anywhere near the engine... )
I believe a fuel polishing system is run before firing-up an engine.
This removes all the contamination before the engine's fuel-pump even starts.
edit 2:
Marine Diesels, in the stuff above...
Also, this is in light of some events written about years ago...
1 was a small jet that lost power at high altitude due to slush-ice in fuel,
another was a jetliner that smashed after the same problem, ttbomk...

slush-ice in the fuel clogged something in the fuel-system, causing...

a drop in power, so therefore the crew...

increased thrust, which caused ALL the engines to clog/die, so the new recommendation was...

if in that type, at high altitude, in cold, if power reduces unexpectedly,
then reduce thrust to unclog the lines, & it should clear...

also many apparently have had problems with ice in fuel messing things up for them in piston aircraft...
also I know some are running automotive-conversions,
& if anyone ever has ethanol-blend gas in their aircraft,
& that ethanol has absorbed water, & gets cold, it can separate out,
leaving 2 distinct fluids in the tank:
ethanol-water & gasoline.
( I'm not saying running auto-fuel is legal in an aircraft,
but rather that I know human-nature. )
edit 3:
that link above includes some interesting stuff
also, the whole idea may be bunk,
if the amount of ice-slush in a jetliner's tanks is measured in tonnes, rather than litres,
as no catching-out device is going to handle that kind of volume.
I don't know what volume is involved.

Depending on what you mean by cruising yachts/boat, the fuels used may differ huuuuugely from what is used in aviation.

A cruise boat is also a heck of a lot heavier than an airplane.

Interesting question, but it looks like you're writing poetry!

It isn't that poetry is the intent, but rather clarity: brain damage makes thinking hard, ANY means of keeping complicated thoughts clear helps!

The simple answer is weight/risk/added complexity: the systems are heavier than they are worth for the problems they avoid in aircraft.
While ice blockage has been an issue for aircraft in the past, planes that fly high enough to warrant it have fuel heating systems to avoid this very issue.
The reality is that the chances of water getting into marine fuel are MUCH higher than water getting into AvGas. Water finds its way into airplanes in mainly one way: warm moist air that fills the space in fuel tanks condenses in the cold and the water precipitates out. This often happens over night when planes are not re-fueled after their last flight and left out in the cold. As such its extra important to sump the tanks for the first flight of the day. You can also mitigate this by filling the tanks every night if possible. Pilots are also taught to diligently sump tanks to avoid the issue in the first place.
In my experience, flying in the north east of the US where the air can get humid and the nights can be cool, I've never pulled more than a few bead size drops of water out of the tanks of my archer in the morning. I know of others that have pulled more but not significantly more.
There have been occurrences of a fair bit (hundreds of gallons of water) getting into aircraft tanks but these have generally been caught and handled. On the bright side we have a few nice things in aircraft that make water easy to deal with.

Water is heavier than AvGas so it will pool at the lowest point of the tank which is generally where the outlet/fuel line is connected.
The lowest point of a fuel tank on an aircraft is fairly easy to get to so pulling a test sump of fuel is no problem during pre-flight
It's fairly easy to deal with the fuel once it's in the sump cup on the ramp, chances are you wont anger the EPA all to much.

On the contrary, with marine fuel tanks it can be hard, if not impossible, to access the sump in any reasonable way and once you drain it you run the risk of it getting in the bilge and ending up getting pumped overboard which the EPA will have an issue with.
On a boat you have lots of options for water to get into the tank since there is generally water all around. Maybe it splashed in some gas cans you had on deck, maybe it splashed in during a mid trip re-fuel, maybe it splashed in refueling at a dock, maybe it was raining one of these times or all of these times, maybe the dock kid put the fresh water hose in the fuel inlet in a haste etc. etc. As such fuel/water separators are far more critical on a boat where there is often space and weight to spare and the chance of water getting into the fuel is high.

My homebuilt has fibreglass fuel tanks (on the wing tips) and I've never had water in the fuel in the 10 years I've had the thing which was always a surprise.  I'm not sure why the difference compared to metal tanks. You'd think that metal cold soaked or fibreglass cold soaked would create the same condensation conditions, but apparently not.

@John K: Where do you live?  I don't think I've ever had condensation in my fuel tanks, but then I live in an area (US intermountain west) where warm, moist air is a rarity.

@Dave  Eastern Canada.  With metal tanks in this part of NA you would expect to find drops of water in the fuel from time to time if parked outside.  On a preflight of a plane like a 172, I made it a habit to shake the plane at the very start to slosh the fuel in the tanks and wash any water droplets off, then delay checking the sumps until the preflight was done to give the water time to migrate to the low point.  You would find water drops that wouldn't appear if you just drained the sumps at the start.

@jamesqf, I don't fly, but I had some training a few decades ago in Allentown, Pennsylvania, U.S.A. I drained an ounce or two of water from the sumps on at least a couple of occasions when I was the first customer of the day. I was not taught to "slosh" the tanks though. Maybe my instructor came from a warmer climate, and had not heard of that trick.

@SolomonSlow I trained out of KDYL with lots of landings at KABE, but the training to not slosh the tanks is what I was always told. It can take a lot of time for the fuel to settle in the tank so I was always told to sump them first before disturbing anything.

@Solomon Slow: But Pennsylvania (or anywhere east of the Mississippi) is one of those places where you have a lot of warm, moist air, at least in the summer.  Grew up not far from there, and still remember the valley fogs we'd get on many summer nights as the humid air cooled and moisture condensed.

Given the way aviation-safety is supposed to work, I'd be interested in someone putting a quarter-fueled small plane out in the cool, to collect condensation, with a light & encapsulated camera in each tank, sump it in the morn, then shake wings & time the collection of dew in the sump, via the vid: data is better than assumptions, right?  Thanks for all these understandings/insights!  ( :

Sheer volume is the reason.
Aircraft use fuel at an astounding rate.
A Panamax-class container ship is enormous - bigger than the USS Iowa or the Essex class aircraft carriers on display at many major port cities. They burn 9900 litres of fuel per hour.
A 777 burns 7.5 tonnes of fuel per hour, or at 800 g/l for Jet A, that's 9375 litres of fuel per hour.
These burn rates are within 6% of each other.
A 777 would need a polishing plant as big as a Panamax freighter's.
That's a big bag of "not gonna happen".  Given that a 777 has complete turnover of its fuel tanks every 24 hours anyway, it simply makes sense to do it on the ground.

"a 777 has (a) complete turnover of its fuel tanks every 24 hours" ... meaning the fuel that is in them is completely used and replaced in an average of that time frame?

CG, I believe Harper simply means, yes, 777s fly continuously (eg back and fore across the Atlantic, or whatever), using all their fuel all the time - they never sit around.

Answering from the yacht perspective... the problem here is diesel bug.
Yachts are often powered by low power 1-cylinder diesel engines, and the engine's main use (for many sailors) being to get in and out of harbour, the main power coming from the wind.
As such, a tankful of fuel may last an entire season, and it may not have been fresh in the pumps to start with, in a smaller harbour or marina. Which is long enough to not just absorb moisture, but for diesel bug to grow. This is bacterial growth, and the problem is even greater with the introduction of biodiesel.
Diesel bug turns the fuel to jelly, clogging pipes and injectors, and a failed engine at sea is a safety problem if there is either too little wind, or too much. Fuel polishing can either eliminate diesel bug or keep it out of the engine. (You can also use anti-bacterial additives)
If JP-4 doesn't suffer from "diesel bug", or fuel turnover rate is high enough that fuel isn't lying in the tank for months, this may simply not be an issue for aircraft (though ice is another matter).
I'm taking a wild guess here that jets fill up more than once or twice a year!

Carnac the Magnificent answers, "propane," to the question, "what fuel will power small outboard motors, and small sailboat auxiliaries in the not-so-distant future?" Maybe not so practical for airplanes though.

@SolomonSlow actually quite a few are going electric, with LiFePO4 battery and solar to top it up, like this (local to me) https://www.victronenergy.com/blog/2014/01/12/new-blogger-john-rushworth/

The technology is advancing. But, for right now, it is limited to prop driven aircraft of limited airspeed, range, and payload capacity.

@DeanF. The reference to going electric was actually in regard to "smal outboard motors, and auxiliaries". But you are  of course correct regarding the current limitations wrt electric aircraft propulsion.

Airplanes range from single seat to 600 seaters, and they have varying levels of technical sophistication. Some or all of the following maybe in use if there's a potential fuel contamination (with water) problem:

Fuel heaters
ice filters
Fuel/Oil/Air/Hydraulic fluid heat-exchangers.
Checks and crosschecks of fuel by fuel vendor and operator before refueling.
physical checks for each tank using purpose built drains plugs.

For airplanes with sweptback + dihedral wings water will collect in the inboard  forwardmost part of the wing tanks for tanks following the wing profile shape. Fuselage/body tanks designed to provide a sump-like section that collects water due gravity. (being heavier than fuel)
Airplanes also face icing problems with engine intakes/nacelles/wings
and  depending on the kind of fuel used, eg Jet, Jet A, Jet A1, JP4, .. . the fuel itself can start freezing depending on the Temperature exposed to, effects of skin friction (due speed through the air), and duration of cold-soak. This happens around -40degC and below - freezing fuel is evidently initially of a soft viscous wax-like consistency.

that sump-like section of the body-tank is what I meant, but I wonder why that jetliner went-down, if it already had that?  So it is the smaller aircraft that don't prevent water/ice in the line from getting past a catch-box, then, it seems...  Thx!

So, my sailboat's tank hold 20 gals. of diesel, and at the end of each season I top her up with 3-4 gals. For an interesting puzzle you can work out the average age of the fuel in the tank, but the point is that a sailboat tends to carry old diesel in a warm, moist environment for extended periods. Meaning that- even with additives and stabilizers- you have ideal conditions for the growth of microbial life in the fuel. This life (technically known as "goo") will, if left to grow rampant, clog your filters to the point where the engine eventually shuts down from lack of fuel. If it's a windy, wavy day, the goo gets kicked up off the bottom of the tank to kill your engine even faster (on precisely the sort of day you DON'T want to dock under sail).
This goo is what fuel polishers remove, not water or ice (you have a water separator on the engine's filter for water in the fuel, the ice is reserved for my drinks). In fact I do have a fuel polisher myself- I don't keep it on the boat though, as it would only clutter the place up. Its the sort of thing you drag out of the garage only once every 3-5 years or so.
As you can see, the point of a fuel polisher on a yacht is for a completely different set of problems than faced by the typical aircraft.
Have a good one!

the specific problem being removed ( bacterial guck vs water/ice ) is different, but the Removing Problems Before They Reach The Engine bit is identical in intent, to me.  Lots of happy sailing!  ( :


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Question About Systemic Culture
I have a question about Systemic Culture in the context of aviation. What is a systemic culture, and how is a systemic culture related to the aviation industry?

This one is easy. Go read the primary cause of the horrific crash of two 747's at Tenerife in 1977, and why the F/O of the KLM aircraft did not override the actions of the alleged highly-experienced captain, Jacob Louis Veldhuyzen van Zanten. Everything can be tied to a systemic culture that severely discouraged such actions, even in the face of an imminent disaster. This accident led to many changes in virtually all western commercial airlines to address this specific issue.

Still a big problem in places like Russia and China, and to a lesser extent, other parts of world outside Europe and the Anglosphere.

@JohnK Yes, I agree.

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How is washout built into a fibreglass wing?
How is washout built into a fibreglass foam core wing of a GA Airplane with 40% span flaps, 40% span ailerons.
Does the angle of incidence change gradually over the span of the wing, or is the airfoil rotated downwards to reduce the angle of incidence eg. at the wing airfoil joints and then just flared, eg. over the span of a 1m to a matching trailing edge?
Eg  20% span root wing aifoil incidence no flap, 5deg;
40% span mid wing airfoil incidence with flap, 4 deg;
40% span wing tip airfoil incidence with aileron, 3 deg

Washout can be geometric (angle of incidence changes over span) or aerodynamic (airfoil changes over span), or a combination of both. The wing station where that washout starts or ends can be freely chosen, so the airfoil and incidence might stay constant over the inner wing and only start at mid-span. The goal is always to shape the lift distribution over span such that stall starts at the wing root or induced drag or root bending moment is limited.
Washout has to be chosen in combination with chord variations over span: While a rectangular wing rarely needs washout for benign stall characteristics, a taper at the tip to 30% of root chord will definitely require some washout.
A fiberglass wing gives the designer full liberty at choosing both aerodynamic and geometric washout by shaping the foam core accordingly. Some corrections in incidence will still be possible while curing the epoxy matrix, but ideally the core will already have the desired twist already.

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Do strike aircraft turn off their datalink?
As far as I know, it is normal procedure for aircraft on a strike mission to go into radio silence at a certain point of the mission, as to not give of any unnecessary emissions that could warn the enemy of the aircraft's presence. I was wondering if this also applies to the datalink system or whether there is some kind of mode for the datalink in which the aircraft only receives datalink information, but doesn't transmit.

As long as it is satellite shared it should be no problem to recieve only. It's the same with the GPS signal, the fighters still recieve it, even when radio transmission is turned off.

But then you could for example not see your wingman on your datalink.

I think there are now some types of secret datalinks. One principle is using laser between the aircraft in the flight, another is using some form of direct spread spectrum to make it indistinguishable from noise for anybody without appropriate key. I am not sure how much either is already deployed.


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Does Wing Area vary with angle ot attack?
For a very basic airplane, say like Cessna 150 is built with Wing Area (S)=15 meter squared (say it 15m*1m). In another part said that the Lift (L)=0.5*rho*(V)^2*Cl*S. Mean, Lift is affected by the wing area. Yes, it is clear. My question, should I consider the wing area as fix area during the take off, cruise, and during landing? If angle of attack of the wing is 15 degree during take off, what is the wing area?
From the Lift formula above that is written here, S (wing area) is planform (projected). Where it to be projected? If like above, if during the take off the Angle Of Attack is 15 degree, what is the wing area? Very appreciate if explanation provided with reference.

Doesn't wing area change as the flaps are extended (takeoff and landing) and retracted?  My airplane for example, I take off with 10 degrees flaps, and land with 30 degrees, but cruise with 0 degrees. The flaps extend back and droop.    Cessna 150 has similar, and I think in some years had 40 degrees of flaps for landing.

Cessna 150L has wing area of
Trainer version: 157 square feet, and Commuter version: 159.5 square feet (different wing tips I think, so wings are 6 inces wider)

Angle of attack of 15 degrees for a Cessna (and most fixed wing aircraft) is either stalling, or right at the edge of a stall. Are you sure this is what you mean (AoA rather than pitch angle)? Typical take-off Aoa is usually less than 10 degrees.

Could you please define the other variables in your equation? V velocity, rho?, Cl?  In the real world, unless the wing is reconfigured, area will not change.  Let's see if the math will fit.

Wing area does not change with angle of attack. The only way wing area can change in flight is if there are devices on the wing that can extend and retract, making the wing longer, shorter or wider.

Sir, after I did long study, wings area is changed with AoA. You must not see from the relative wind side, but from the Lift, from top of the wing. Lift (L)=0.5rho(V)^2ClS. Now, we talk about the S. As surface area (S) is opposes the gravitational force while Lift (L) is orthogonal to the wing, then the surface area must be multiplied with cos(AoA). Just need to open Google to see the force component here, which F * cos (AoA) is Lift (oppose the m * g), and F * sin (AoA) is induced drag.

Of course lift changes with AoA. But Lift <> Wing Area.

@AirCraftLover, your mistake stems from the assumption that "Lift (L) is orthogonal to the wing". This is wrong. Lift, by definition, is orthogonal to the wind (and drag is along the wind). Gravity has nothing to do here whatsoever. ALL the aerodynamic forces/coefficients are calculated in the wind axes. Lift is linear wrt angle of attack only in the wind axes. Wing area is the "working space" of the flow, so to speak, and so its area is not changing with $\alpha$. Only with this condition lift is linear with $\alpha$, which is the most useful and gratifying property in aerodynamics.

Simple answer: the surface area is the area of the wing when you look at it straight down. The question then of course is, why?
The answer is quite trivial: because it's easier that way. In a way, your idea that the lift is dependent on the wing area projected in the direction of the incoming wind seems quite reasonable (surely, this is what the incoming air "sees"). This projected area equals
$$S_p=S\sin(\alpha)$$
A good reason not to use $S_p$ is that we like the equation to contain real geometric parameters, so that we can easily scale our equation up and down. So, why not define the lift equation as
$$L=\frac{1}{2}\rho c_l S\sin(\alpha) v^2$$
This looks nice right? Everything is in there, even the angle of attack!
Sadly, curve of the lift versus the angle of attack does not follow a nice $\sin(\alpha)$ curve. This equation is thus sadly not only misleading, but you would have to divide all existing lift curves by $\sin(\alpha)$, which would make them erratic (especially around $\alpha=0$) and much less insightful. So, lumping the angle of attack into the lift coefficient is in the end the best way to go.

Either that or only consider one angle of attack at a time and take Cl off the graph.  "taking a bigger bite of air" would go towards drag, which is on the L/D graph.  No need for sadness, you engineers do a great job getting
us in the ball park before a single model is built and tested.

@sanchises, wings area is changed due to AoA change. See my comment to Robert DiGiovanni below and Juan Jiminez above. See the area changed related to the lift, which lift is oppose the gravity, while Lift is orthogonal to the wing. This is make sense. The surface area is projected to the earth (parallel to the gravity).

@AirCraftLover I disagree. It's not a question of geometry, but a question of definitions. The wing area is defined as the chord length times the span length. The apparent shortening due to AoA is factored into your typical $C_L$ graphs.

Yes, I maybe lack in defining my question as lack of my understanding. But after I read again my question, the last paragraph is clearly I asked about the projection, "where it to be projected".

@AirCraftLover I understand, but I maintain that S should be projected at 0° AoA at all times, or equivalently perpendicular to the wing chord line (at least if you're planning on using any available data for $C_L$).  The gravity and lift vector do not matter, because $S$ is defined as a geometric constant and should never change during flight.

In my understanding as newbie in aircraft, the maximum wing area is when the AoA = 0, as it will produce maximum value of cosine. In the wikipedia here, surface area (S) is defined as the planform (projected) wing area. Thus, the projection make the change. But that open me a new question, if I have projected the planform wing area, while coefficient of lift is clearly related to the AoA, should I use two time the AoA effect?

Or, is any mistake with the statement in wikipedia regarding the surface area (S) is defined as the planform (projected) wing area explanation? This is not easy for me to understand.

@AirCraftLover Wikipedia is not talking about a projection that changes in flight. You should take that statement as "not the wetted area". That is, you don't count the bottom and top surface separately, and you don't take into account the extra skin surface needed to create the airfoil thickness. You just look straight down (once) on the wing so that all you see is the chord length and span length.

Here is the 150M planform, you can see the flaps from the fuselage out, a foot or so wider than the elevator.

The 150 uses Fowler flaps, described in Wikipedia:

Fowler flap
A split flap that slides backwards, before hinging downward, thereby increasing first chord, then camber.[13] The flap may form part of the upper surface of the wing, like a plain flap, or it may not, like a split flap, but it must slide rearward before lowering. As a defining feature - distinguishing it from the Gouge Flap - it always provides a slot effect. [14] Invented by Harlan D. Fowler in 1924, and tested by Fred Weick at NACA in 1932. They were first used on the Martin 146 prototype in 1935, and in production on the 1937 Lockheed Super Electra,[15] and are still in widespread use on modern aircraft, often with multiple slots.

https://en.wikipedia.org/wiki/Flap_(aeronautics)#/media/File:Airfoil_lift_improvement_devices_(flaps).png
I can't find numbers on how much the chord/camber is changed on a 150.
Here's a great discussion of the Fowler flap from 1942
https://www.flightglobal.com/pdfarchive/view/1942/1942%20-%200783.html

Actually my point with my question is, should the wing area changed with the angle of attack (AoA), as there is mention as in the Wikipedia that the Wing Area (S) is the area of the projected wing. Projected is the wing area we see if we see from above parallel to the gravity's direction. If it is like so, then the wing area will be depend and the AoA's of the airplane, it will be smaller when it is climb (pitch up) or landing than when it is being cruiser, moreover when it is being park.

An analysis of the variables shows Coefficent of Lift, CL, varies with change in angle of attack. ρ is air density.  So, check your AoA/CL graph.  Area should be constant.
L = 0.5 * ρ * V2 * CL * S
Post Script:  this equation may be of value if one wanted to swap airfoils in a design.  For AOA comparison of lift, one might make a giant constant out of the entire equation (L) and the run various AOA off the AOA/Cl graph.  Although laborious by hand, this would be tailor made for a spreadsheet and would make a nice presentation with graphics.
Also, if anyone knew if coefficient of lift for an airfoil was done at a specific AOA by convention, this would be extremely good information.  I would imagine it may be done at AoA for best lift/drag ratio.

Yes, it is. After I did long study, wings area is changed with AoA. We must not see from the relative wind side, but from the Lift, from top of the wing. Lift (L)=0.5rho(V)^2ClS. Now, we talk about the S. As surface area (S) is opposes the gravitational force while Lift (L) is orthogonal to the wing, then the surface area must be multiplied with cos(AoA). Just need to open Google to see the force component here, which F * cos (AoA) is Lift (oppose the m * g), and F * sin (AoA) is induced drag.

Force components change with angle of attack (and also with bank ), but this does not change wing area.  However, on terms of lift, I see how you might call it EFFECTIVE wing area based on the VERTICAL lift component, opposing m×g.

That probably the word should be, the effective wing area. In my question I asked, where the wing area to be projected. That was confusing me as I read in wikipedia.

Dear Robert DiGiovanni, in calculation, how to use the projected wing area and the coefficient of lift (Cl)? As we know, the Cl is related to the AoA. (Here is explained that the surface area (S) is defined as the planform (projected) wing area)). But at the same time, the Lift Coefficient is different for every AoA, as also explained in that link.

It is true that F x cos(AoA) will have a higher percentage of Total lift vector at lower AoA, but remember Total lift vector gets much bigger as AoA increases, right up to stall. Now what we need to find out is what the Lift value on lift vs AOA and lift vs drag charts is!  Is it total lift or cos(total lift for that angle).  I bet @Sanchises or Jan Hudec knows!

Yes Dear, thank you for invited @Sanchies and Jan Hudec, hopefully they can explain.


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Can a human get sucked into a jet engine?
Can a human get sucked into the jet engine of a normal modern airliner? if so has it ever happened and what is the minimum or maximum weight that these engines can suck? As a safety measure, wouldn't light weight but high strength retracting safety covers that cover engines when the aircraft is parked protect both humans, equipment and engines? Of-course it would have to take into account the need to minimize weight. Also it could have the option to be controlled by the ground team supervisor remotely as an extra safety measure.

Relevant: http://aviation.stackexchange.com/questions/9680/why-not-mount-airliner-jet-engines-above-the-wings

Yes, it has happened, and the resulting photos are pretty gory. Would've been quick, though, at least. http://message.snopes.com/showthread.php?t=60975

I suppose then that airport design incorporates the sucktion powe of jet engines

https://xkcd.com/1097/

It's actually more than just weight.  Surface area and density would also play a part.  A 100kg lead brick might be safe at a given distance (from pull) whereas a 100kg human might not.  A 100kg human might be safe at a given distance that a 100kg hang glider would not.

Yes. Human beings can get sucked into jet engines if they are close enough- this has happened multiple times in a number of aircraft ranging from A319 to A6E intruder.
However, it happens only in rare cases- usually in case of miscommunication or a mistake, when safety procedures are not followed. The following image shows the safety hazard area for aircraft engines.

A warning poster, available from Boeing, reminds ramp and maintenance workers
about the dangers of engine ingestion; image from Boeing Aero
In addition, the engines also have hazard-area warning decals on the nacelles to warn the ground personnel of the dangers.

Warning signs on engines; image from Boeing Aero.
As for the maximum weight that can be ingested, it will vary with the engines, though they have been known to ingest items from safety pylons to baggage containers, and of course people.

That first image is bad in a way.  It has the "DO" list under the do not diagram and the "DO NOT" list under the do diagram.

@KevinRubin You can always sue them for using bad infographics after you’ve been sucked in and died. ;)  (+1)

There's actually a guy that survived this once (not graphic, although somewhat chilling, but be warned the YouTube sidebar may have a few tasteless thumbnails). Some of the ... darker corners of the internet do have some graphic descriptions of these types of events with poorer outcomes, though.

True story: Boeing actually used a guy on a tether to collect the data to determine the radius of that safety arc, at least for the 737s. My father was the man on the tether. We used to have a video of it.

Holy cow. Now there's a tether I'd want to quintuple-check before the test.

@KevinRubin sounds like a job for http://ux.stackexchange.com/

True story. ICD-10 standardized medical billing codes have a code for a person sucked into a jet engine. V97.33. There are also spin off codes if it's the first, second, or subsequent doctor you have visited for this injury: http://www.nuemd.com/icd-10/codes/V97.33. I am told, only rumor, this code was created because someone actually survived the experience.

@KevinRubin http://ux.stackexchange.com/questions/102715/on-a-warning-sign-describe-safe-actions-near-pictured-danger-or-pictured-safet

Other than for extra safety, is there a particular reason the danger zone extends past the side of the inlet on the infographic form boeing? Could someone standing beside the engine really be sucked in to the inlet on the front?

@KevinRubin - My first thought as well!

@Ksery The engine’s suction power pulls some air in from the sides.

what is the minimum or maximum weight that these engines can suck?

Quite a lot, considering they can ingest ramp equipment...

This is a JAL 747 ingesting a baggage container.

Delta L-1011 doing the same.

They should really feed their planes more often! Maybe they wouldn't try to eat the containers

I like how the container almost perfectly fits in the engine. It really makes the picture work. Also do you have a link to more info on this incident?

@DavidGrinberg considering some of the engine sizes on more modern jets, if this were to happen with a 777, 787, A380, or A350 then you would be looking at a shredded container and engine, not just a stuck container :)

@DavidGrinberg almost like they were designed for it, right?

Were the engines functioning on idle or was the thrust enough to at least power the plane while taxing?

It's happened before, both with civilian and military aircraft.
This video was shot in 1991.  Crews ready an A-6E attack aircraft for launch aboard Theodore Roosevelt (CVN-71) for a night sortie over Iraq during Operation Desert Storm when a fatigued green shirt walks in front of the port jet intake at full power.  He is one of the few people who had this happen to them and live to tell the tale.

how can he survive such intense impact?

@LưuVĩnhPhúc He was wearing a helmet, and it was a small intake. Lucky guy, for sure.

The story was that his float coat, the life vest uniform that all flight deck hands wear, got snagged on an air date probe at the front of the intake duct, which prevented his body from being ingested into the compressor.  Other parts of his kit came loose and were ingested into the engine as FOD, destroying it.  He was very lucky, but got pretty badly banged up in the ordeal.

Longer video on this incident: https://www.youtube.com/watch?v=GF3Iz7b95-8

@ceejayoz, the helmet was of no help (it got sucked off his head anyway).

Yes. Here's an incident that happened at Mumbai (India) Airport in December 2015. A technician was sucked into the engine and killed.
A news report of the incident and AvHeald report for completeness

A Vacuum Cleaner for an Intake
The A7-E was notorious for swallowing people on the carrier deck. In the picture below the Yellow Shirt standing in front demonstrates how low and large the intake to the turbofan engine is. There was a lot of activity on the deck especially during launches and recovery, and it was easy to step in the wrong place. We were always cautioned, over and over again, be aware of the intake.
Luckily most of the time I was around the A7-E it was not turning. I would do my preflight at the start of the flight. At the end of the flight, with the engine shut down, I would come down off the ladder and do the post-flight. I turned and headed around the nose, and worked my way back and around the air frame.

Danger Areas for Suction, Exhaust, and Radiation
The danger areas are shown in the diagram below, where:

Yellow is idle power
Red is military power
The pink is the radiation (radar operating) danger area

Notice that the suction danger area at idle power extends out to 15 feet.

Hot Seat and a Close Call
As deployment neared the operations at the field shifted over to carrier qualifications. When arriving aboard the ship a pilot would have to qualify by performing a number of day and night landings. Each pass we made at the ship was graded. We started practicing at the field, and the schedule might use a procedure known as hot seating to maximize the number of pilots trained.
A pilot would start the aircraft and head for carrier landing practice. The aircraft had been previously fueled to keep us somewhere below our maximum landing weight. This was around 5,000 pounds. The pilot would finish the required number of approaches and on the way back to the squadron's apron hot fuel at the airfield fueling area. The term "hot fuel" was used to describe  that the aircraft was turning while getting fuel. Once back at the squadron the crew would chock and tie down the aircraft. The pilot remained strapped in with the aircraft turning at idle.
The next pilot to fly would meet the aircraft as it came in, and do his  preflight inspection, being careful to stay away from the danger areas. We would duck under the tail, and not cross close in front of the aircraft. When the next pilot was ready they came up beside the cockpit ladder and exchanged hand signs with the seated pilot. The pilots would exchange places.
The pilot finishing would then do their walk-around for the post-flight check. One night, after getting down off the ladder I did what I routinely do, which is head around the nose of the aircraft. It was dark on the tarmac, and I hadn't finished one step before I felt a hand grab me by the survival vest and pull me back hard, almost off my feet. I owe my life to that Maintenance Officer.

Why is the uncontained-engine-failure danger area only shown for the max-power condition, and not for idle?

Not exactly sure, but I would guess because the area shown is the max area subject to the catastrophic failure, and at idle the area will be smaller. Again, not sure why.

@Sean the engine casing is strong enough to contain a turbine failure at idle, but at full power there’s so much energy it would rip straight through it.

Yes, humans can get sucked in. Yes, they have been sucked in. What can get sucked in is a factor of its size, surface area, and weight, (just like an airplane) but it really depends on the situation as to how an object comes to be ingested into such an engine. :-)

I remember somebody being sucked into an engine in 1989 with the accident involving United Airlines flight 811. The forward cargo door blew out, causing the cabin floor to cave in.https://en.wikipedia.org/wiki/United_Airlines_Flight_811
At least they found body parts in one of the engine - 9 people died in that incident.
I remember it because it was en route from Hawaii to Auckland New Zealand (where I live) and a journey we had made several times.

I'm guessing OP is asking about it happening on the ground. It shouldn't be too surprising that a jet engine will suck in anything in its path while in the air.

@fooot yes, it would be a rare case where people are outside the aircraft fuselage during flight.  Skydivers exit behind the engines, and emerjency eject/bailout routes would take engine intakes into consideration.

Great answers already here, I'll just address the "minimum weight" part of the question.
There is no minimum weight. Foreign object damage is a very serious safety concern in aviation, because an engine can suck up pretty much any random object.
I've seen the crowd addressed en masse in air shows to please mind their garbage for the safety of the performers.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

authors: Bob Jarvis - Слава Україні


text:
Do airliners perform a dive maneuver to reduce altitude
DO airliners, jumbos included, like the Airbus A380 and Boeing 747 routinely perform dive (nose down) maneuvers to descend or do they rather reduce speed and descend with the nose up? If not, why not?

Dives are done in emergency. Why dive if you can smoothly and comfortably descend along a slope? (But your comment about nose up is a bit puzzling, do you define "diving" as anything with a nose down?)

Yes that is what I define diving

Then just a terminology note: "diving" usually refers to a rapid descent, otherwise you simply speak of a descent.

Do they perform dives to reduce altitude? Yes, in certain emergency situations. Is this a normal procedure? Not unless it's one of those emergency situations.

The described procedure resembles the combat approach, which can be done by military cargo planes to remain as long as possible out of the range of small arms.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Is Assumed Temperature used in conjunction with a Derate in the B737 NG?
When using an Assumed Temperature for Takeoff, is it common operational practice to also use a Derate?

Yes, that is allowed.
You can combine selection of a fixed derate and an assumed temperature for the takeoff thrust on the FMC N1 Limit page, but only up to a reduction of 25%.

Takeoff Derate
Fixed derates can be selected on the N1 LIMIT page. [...]
Derated takeoff rating can be further reduced by assumed temperature. [...]
Assumed Temperature Thrust Reduction Takeoff
A takeoff thrust less than the full rated thrust may be achieved by using an
assumed temperature that is higher than the actual temperature. The desired thrust
level is obtained through entry of a SEL TEMP value on the N1 LIMIT page or
TAKEOFF REF page 2. [...]
The maximum thrust reduction authorized is 25 percent below any certified rating. [...]
If the assumed temperature method is applied to a fixed derate, application of
additional power should not exceed the fixed derate N1 limit as loss of directional
control could occur while on the ground.
When the assumed temperature method is used with full rate, the reduced thrust
setting is not considered a limitation. If conditions are encountered where
additional thrust is desired, the crew can manually apply full thrust.

(Boeing 737NG FCOMv2 11.32.3 - Flight Management, Navigation - Flight Management Computer)
You can see the current selection on the Upper Display Unit:

2 Thrust Mode Display
[...] Thrust mode display annunciations are:

TO – takeoff
TO 1 – derated takeoff one
TO 2 – derated takeoff two
D-TO – assumed temperature reduced thrust takeoff
D-TO 1 – derate one and assumed temperature reduced thrust takeoff
D-TO 2 – derate two and assumed temperature reduced thrust takeoff

(Boeing 737NG FCOMv2 7.10.2 - Engines, APU - Side by Side – Displays)
What would actually be used by an airline depends on the exact situation. The derate and the thrust reduction via assumed temperature are not the same thing because the derate affects Vmcg, but the assumed temperature does not (see also What is the difference between Assumed Temperature and Derate takeoff thrust?). Today, most airlines will use an EFB (or a separate tablet computer) to perform the TO calculations and the computer will optimize the thrust reduction while taking all legal requirements for V1 (which may be affected by Vmcg, which is a lower limit for V1), second/fourth segment climb gradient, obstacle clearance and possibly noise reduction into account.

The maximum 25% reduction limit refers to %N1? So if a Max power Takeoff is calculated at 98.0 %N1, the maximum reduction can be as low as 73.5% ? I find this to be an extremely low power setting. Or does the 25% limit refer to Engine Power and not %N1?

Yes, that refers to %N1, but not based on the calculated max. takeoff (98% in your example). It is based on the certified rating thrust for that engine, which you can find in the TCDS (Type Certificate Data Sheet). I don't think it is extremely low, if you consider that the OEW of a 737-800 is ~41t and MTOW is ~79t. With such a large range of possible TO weight, you also want a large range of thrust.

@StamatisVellis Just realized I was slightly wrong in my last comment: it is not technically 25% reduction in N1, but rather a 25% reduction in actual thrust. Since thrust and N1 are not perfectly proportional (see e.g. this image), this may not be equal to 25% less N1, but it is somewhat close.

Yes, both can be used together, allowing actual thrust for takeoff to be much lower than simply 25%. Mostly, Operators prefer the lowest possible thrust so as to have longer engine life, more time on the wing in regular service than off the wing in maintenance.
A simple visualization of the derate is to pretend there's a smaller, less powerful engine on the wing and the airplane performance certified accordingly.
Typically:
Max Assumed Temp on ‘No derate’ is 100 - 25 =  75% of full thrust
Max Assumed Temp on ’10% derate’ is 90 - 22.5 = 67.5% of full thrust
Max Assumed Temp on ’20% derate’ is 80 - 20 = 60% of full thrust
Even at 60% of full thrust, the N1 remains in the higher 80’s for anything I’ve flown. There’s no simple linear relationship between the reduced N1 and percentage reduction of thrust. Also note that the N1 for 100% thrust - No derate, No Assumed Temp - is normally more than 100 and the red line N1 limit higher than that.

Indeed. I just made the calculations for maximum allowed Assumed Temperature (67 degrees) plus maximum Derate (22K) for the 737-800W/CFM56-7B26, under Sea Level, ISA conditions. The minimum %N1 (i.e maximum derate) I came up with was 86.1% N1


text:
What is the difference between GNADIRS and ADIRS on the A320 family?
What is the difference between GNADIRS and ADIRS on the overhead panel of the A320 family?

I would guess with or without GPS..  Perhaps this might help? (https://www.smartcockpit.com/docs/A320-Navigation.pdf)

I'm not aware of this term for A320, there is no reference in the FCOM and FMGC manual I have.


text:
Why did flight AC8823 not land in Washington and why fly to Toronto?
My family and I were in Washington D. C. Reagan airport waiting for the Air Canda 8823 on 14 March 2023 (the aircraft that was supposed to fly us back home to Montreal).
I was following the flight on Flightradar24. Three hundred feet before touching down the plane executed a go around and diverted to Toronto. The airline blamed high winds even though every other plane seemed to be able to land. Why did they divert to Toronto instead of a nearby alternate and why not back to Montreal?

Yesterday's METAR confirms that it was very windy during the time they arrived ("KDCA 141952Z 31021G33KT ..." and "KDCA 142052Z 30019G40KT ..."), but other than that, I'm afraid we could only speculate...

I don't have a definite answer, I suspect its due to immigration considerations.

Although this may not fully answer the question, I post this information as such because it looks into the cause (high wind) provided as a reason by the airline, and it is too much for a comment. If any user want to reuse this text as a basis for a more elaborate answer, please feel free to do so.

The aircraft initiated the go-around at approximately 20:15 UTC, from a height of 300 ft.
Other aircraft were able to land in the 30 minutes before and after the occurence. Most did on the first attempt, a few needed a second attempt.
The primary landing runway at the time was RWY 01, few aircraft circled to land at runway 33.
The weather according to the METARs around that time:

METAR KDCA 141952Z 31021G33KT 10SM BKN060 06/M09 A2990 RMK AO2 PK WND 28035/1921 SLP123 T00561089=
METAR KDCA 142052Z 30019G40KT 10SM BKN055 06/M09 A2991 RMK AO2 PK WND 28040/2043 SLP128 T00561089 53006=

The wind was from a direction of 300 to 310 degrees at around 20 knots, with gusts up to 40 knots.
Peak winds (measured during the past hour) were at 35 knots at 19:21 and 40 knots at 20:43 UTZ. These peak winds were from a more westerly direction of 280 degrees.
A gust from 280 degrees at 40 knots would be a 40kt crosswind component on RWY 01.
The same gust would be a 26 knots crosswind component on RWY 33.
The demonstrated crosswind component on the Embraer 170 is 28 kts sustained, with gusts to 38 kts on dry runways. On wet runways, the demonstrated crosswind component   is 28 kts.
The conditions during the time of final approach were close to the maximum demonstrated crosswind, but probably not exceeding it.
Dulles airport (IAD) has a runway 30, with almost no crosswind component at the time.
I will not speculate to the reasons why no second approach was attempted, and why a diversion back to Canada was decided.

They always put in the statement "not considered limiting" on x wind limitations so it remains the Capt's judgement call, and some will go for it and some won't.

@JohnK indeed. It is a maximum demonstrated value, not a limit. So as the captain, at your own discretion, you can decide to attempt a landing in a stronger crosswind. But it is not easy to explain in front of the investigation committee why you, as the captain that crashed the aircraft, thought you were better at cross wind landings than the test pilots.

@JohnK While the manufacturer's AFM manual landing crosswind is demonstrated and not limiting, company policy typically dictates a limit. I am pretty sure AC's policy is limiting. Company policy may also further limit based on FO flying and low-time pilots. Autoland is also a AFM limit, and significantly CAT II and CAT III operations have a 15 kt limit set by the FAA (OpSpec C060) due to the design of ILS.


text:
Are there any twin-engine turboprop airplanes with FADEC and 6 seats?
Are there any twin-engine airplanes with FADEC with 6 seats? Is there nothing equivalent to DA62 in the turboprop world with slightly bigger interior and club seats?

There are currently no General Aviation twin turboprop aircraft with FADEC. Turboprops have always had separate power levers and propeller condition levers.
I believe the first GA turboprops with FADEC are the single engine Pilatus PC-12 NGX  and TBM 960.


text:
What is the minimum weight aircraft in which someone can build logged flight time?
What is the minimum weight aircraft in which someone can build logged flight time? Is logging flight hours in an ultralight possible?

Welcome to aviation.SE! Which country or regulations are you asking about?

@Pondlife I added a tag. Should my question have it?

What type of flight time?

There is no weight limit, requirement, nor restriction for logging time in a logbook. However, there is a requirement to only fly aircraft that are properly certificated, registered, and airworthy regardless of if you log the time or not. Part 103.7 allows ultralights to fly without certification or registration. If you are flying an aircraft not meeting certification, registration, inspection, and airworthiness standards, you are flying illegally unless it meets the weight, horsepower and other criteria of Part 103.1.

§103.7 Certification and registration.
  (a) Notwithstanding any other section pertaining to certification of aircraft or their parts or equipment, ultralight vehicles and their component parts and equipment are not required to meet the airworthiness certification standards specified for aircraft or to have certificates of airworthiness.
(b) Notwithstanding any other section pertaining to airman certification, operators of ultralight vehicles are not required to meet any aeronautical knowledge, age, or experience requirements to operate those vehicles or to have airman or medical certificates.
(c) Notwithstanding any other section pertaining to registration and marking of aircraft, ultralight vehicles are not required to be registered or to bear markings of any type.

Combining this with Part 61.51(j) would prohibit the logging of ultralight experience gained today for the purpose of initial certification or currency.

(j) Aircraft requirements for logging flight time.
  For a person to log flight time, the time must be acquired in an
  aircraft that is identified as an aircraft under §61.5(b), and is—
(1) An aircraft of U.S. registry with either a standard or special airworthiness certificate;
(2) An aircraft of foreign registry with an airworthiness certificate that is approved by the aviation authority of a foreign country that is a Member State to the Convention on International Civil Aviation Organization;
(3) A military aircraft under the direct operational control of the U.S. Armed Forces; or
(4) A public aircraft under the direct operational control of a Federal, State, county, or municipal law enforcement agency, if the flight time was acquired by the pilot while engaged on an official law enforcement flight for a Federal, State, County, or Municipal law enforcement agency.

Furthermore, Part 61.52 does not allow for the logging of ultralight experience gained today for the purpose of initial certification or currency.

§61.52 Use of aeronautical experience obtained in ultralight vehicles.
  (a) Before January 31, 2012, a person may use aeronautical experience obtained in an ultralight vehicle to meet the requirements for the following certificates and ratings issued under this part:
(1) A sport pilot certificate.
(2) A flight instructor certificate with a sport pilot rating;
(3) A private pilot certificate with a weight-shift-control or powered parachute category rating.
(b) Before January 31, 2012, a person may use aeronautical experience obtained in an ultralight vehicle to meet the provisions of §61.69.
(c) A person using aeronautical experience obtained in an ultralight vehicle to meet the requirements for a certificate or rating specified in paragraph (a) of this section or the requirements of paragraph (b) of this section must—
(1) Have been a registered ultralight pilot with an FAA-recognized ultralight organization when that aeronautical experience was obtained;
(2) Document and log that aeronautical experience in accordance with the provisions for logging aeronautical experience specified by an FAA-recognized ultralight organization and in accordance with provisions for logging pilot time in aircraft as specified in §61.51;
(3) Obtain the aeronautical experience in a category and class of vehicle corresponding to the rating or privileges sought; and
(4) Provide the FAA with a certified copy of his or her ultralight pilot records from an FAA-recognized ultralight organization, that—
(i) Document that he or she is a registered ultralight pilot with that FAA-recognized ultralight organization; and
(ii) Indicate that he or she is recognized to operate the category and class of aircraft for which sport pilot privileges are sought.

Weight is not a factor in logging time. And, there is no prohibition against putting things in your logbook that can not be counted for the purposes of initial certification or currency. Although, care should be taken with this. Your logbook is your property. However, your certification gives the FAA the right to inspect your logbook however it chooses. I have co-pilot time logged in a turbine-powered helicopter that I can never count towards anything.
There is also no prohibition against getting an ultralight registered and certificated as airworthy. It might be a lengthy and expensive (and probably improbable) endeavor. But, as soon as you do, it becomes an ultralight no longer according to Part 103.1

§103.1 Applicability.
  This part prescribes rules governing the operation of ultralight vehicles in the United States. For the purposes of this part, an ultralight vehicle is a vehicle that:
(a) Is used or intended to be used for manned operation in the air by a single occupant;
(b) Is used or intended to be used for recreation or sport purposes only;
(c) Does not have any U.S. or foreign airworthiness certificate; and
(d) If unpowered, weighs less than 155 pounds; or
(e) If powered:
(1) Weighs less than 254 pounds empty weight, excluding floats and safety devices which are intended for deployment in a potentially catastrophic situation;
(2) Has a fuel capacity not exceeding 5 U.S. gallons;
(3) Is not capable of more than 55 knots calibrated airspeed at full power in level flight; and
(4) Has a power-off stall speed which does not exceed 24 knots calibrated airspeed.

Very thorough, very good. Thanks

requirement to only fly aircraft that are properly certificated, registered, and airworthy What do you mean by this? Sounds like you’re saying that a licensed pilot is not allowed to fly an ultralight.

@TomMcW - The entire paragraph from which this quote was taken is in regards to logging time to meet certification and/or currency requirements. So yes, I am saying, today, a licensed pilot can not fly an ultralight to log time for those purposes. However, any person can operate an ultralight regardless of whether they have an airman and/or medical certificate. And, since your logbook is your personal property, you can use it however you choose. Just as long as the required information is there upon inspection. Although, I would hazard against extraneous info.

@TomMcW - Part 61.5(j) Does not allow you to log flight time in a Part 103 aircraft for calculating flight time for Part 61 use. Part 103.1 prohibits you from flying an aircraft under Part 103 use if that aircraft is registered and/or certificated as an aircraft category, class, and/or type listed under  Part 61.5(b). As a properly certificated pilot, you can fly whatever you want. Just remember, after January 31, 2012, what happens in 103, stays in 103.


text:
How to calculate the TAT (total air temperature) when a rocket is flying to space?
I checked this answer and I used the formula this answerer provided, but I couldn't get the data he/she presented in the graph. Did I do something wrong?

How can we address "did I do something wrong" when you don't show us what you did?  As they teach in 6th grade math, show your work.

Since you didn't show your calculation / results I can only assume what went wrong. Something easily missed is using the correct units for the calculation. The formula
$$ \frac{\text{TAT}}{\text{SAT}} = 1 + \frac{\gamma - 1}{2} M^2 = 1 + \frac{1}{5} M^2 $$
only works for TAT and SAT as absolute temperatures. You have to use Kelvin (or degrees Rankine), not degrees Celsius (or Fahrenheit), for the calculations.
For the plots shown in the answer, I did all the calculations in Kelvin and then converted the results to degrees Celsius. Try repeating your calculation in Kelvin and see if you get consistent results.
Additional Note: since you want to use this calculation for a rocket flying to space, note that the formula only really works when air can be approximated as an ideal gas. Additionally, $ \gamma = 7 / 5 $ only holds for diatomic gases. At some altitude, these assumptions are no longer useful approximations, so you cannot use this formula all the way to space.


text:
Commercial Operator vs Air Carrier
What is the difference between a commercial operator and an air carrier?  What certificates do you need for both? I saw somewhere online that you need an operating certificate for both air carrier and commercial operator, but then when do you need an air carrier certificate?

Maybe this post helps: What is the difference between an air carrier and a commercial operator??

Yeah but that post says you need an operating certificate for both air carrier and commercial operator but I thought air carriers used an air carrier certificate and not an operating certificate. I understand both are under 119.

This is a very broad question as it's worded.  These terms have both generic definitions and specific ones, and they are sometimes used interchangeably in casual conversation.  If that linked question didn't answer it for you perhaps you need to narrow it down, or help us understand your reason for asking.

I would like to know for my own understanding.

In broad general terms, "commercial operator" just means an operator who works for pay.  This could be a crop duster, flight school, or major international airline.  (Not limited to aviation, a backhoe operator meets this definition...)
An "air carrier" is an operator who carries things by air - passengers or cargo.
Every air carrier is also a commercial operator, but not every commercial operator is an air carrier.  The specific FAA operating certificate required depends on factors beyond these basic definitions.
For example, a flight school could be certified under part 141, or could offer instruction under part 61.  An airline offering scheduled passenger service would need an operating certificate under either part 135, or 121.


text:
What is this contraption off the wing of a US Navy DHC-6?
I came across this image of a US Navy CIRPAS (Center for Interdisciplinary Remotely Piloted Aircraft Studies) DHC-6 Twin Otter.
On one wing there seems to be a thing attached with a few pods and holes. It doesn't seem to be there on the other wing. Does anyone know what this is?
Seems to be some sensor array but for what all exactly? What's the data it collects?
Image of the same is below -

That's a contraption all right.

@DarthPseudonym Looks more like a doodad to me.

That's clearly a chemtrail generator

It's an NSA mind-reading thingamajig!  Better get out your tinfoil hat

@Richard Don't be ridiculous. That is obviously too small to be a chemtrail generator.  That is an infuser that injects the chemicals into the water used to create the chemtrails, not the chemtrail generator itself

It for scientific missions related to the atmosphere, e.g. to evaluate the impact of aerosols on different atmospheric elements like anvil-cirrus cloud formation or storms development.

Source.
Aerosols' effects are not well known, but they might be a large contributor to radiative forcing (global warming) as they play the role of seeds for cloud formation. This field has been actively researched for decades.
Some sensors during one of the missions:

Source.
One of the sensor in your picture (passive cavity aerosol spectrometer probe),

PCASP 1, source. It's a spectrometer:

Sample air enters the forward-facing inlet and decelerates by ~10x. Side-facing skarf tube provides suction for continuous flushing of the air to provide fast time response.

The instrument is used to determine the:

Size distribution and concentration of aerosol particles ~0.1 to 3.0 micrometer diameter in 30 size bins

This aircraft (N83NX), like the instruments attached to the hardpoints, has been used by different US entities, both military and civilian. See CIRPAS Platforms, Instrumentation in Demand

Twin Otter (DH-6) research aircraft operated by the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) at the Naval Postgraduate School in Monterey, California. The aircraft supports atmospheric and oceanographic research for Office of Naval Research, National Science Foundation, Department of Energy, National Oceanographic and Atmospheric Administration, NASA, and others. (Naval Postgraduate School)

Source.
It is currently flying as 76-2256 for the Naval Postgraduate School’s (NPS) Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS), a school of the US Navy:

Source.

Reminds me of when DeHav Canada tried to market a counter-insurgency Twin Otter that had hard points for rocket or gun pods, A NightSun searchlight, an optical gunsight for the pilot, plus a slide-out .50 cal shooting out the folding cargo door.  A chum actually went on gunnery runs with it as a copilot. Don't think they sold any.

@JohnK Sounds like an update, slightly lighter, version of the AC-47. Probably could be pretty effective in a world without MANPADS.

Oh a much much lighter version of an AC-47. But also able to attack directly, not just orbit a target.

Those are instruments used in the jaw-breaking multi-level acronym  RACORO (Routine ARM (Atmospheric Radiation Measurement) Aerial Facility (AAF) Clouds with Low Liquid Water Depths (CLOWD) Optical Radiative Observations) study which was

an investigation of continental boundary layer clouds

Run by the US Department of Energy.
It had many instruments (not all at the same time):

CAPS (Cloud, Aerosol Precipitation Spectrometer)
FSSP (Forward Scattering Spectrometer Probe)
2D CIP (2D Cloud Imaging Probe)
2D-S (2D Stereo Probe)
CIN (Cloud Integrating Nephelometer)
LWC (Liquid-Water Content; Gerber, CIN, SEA, CAPS Hot Wire)
CPCs (Condensation Particle Counters)
etc

For a complete list see the RACORO Data Guide

I guess it's an improvement over RARMAAFCLOWDORO, technically...

So this is how they measure chemtrails then, rather than creating them ?  :¬)


text:
Who issues the Type Certificate in the UK?
Who issues a type certificate in the UK, I think in the US it is the FAA?

Summary: Aircraft type certificates in the UK were issued by the European Aviation Safety Agency (EASA) until January 2020. Since February 2020 they are issued by the UKs Civil Aviation Authority (CAA).

In the European Union, all aircraft type certificates are issued by EASA since 2003:

Before a newly developed aircraft model may enter into operation, it must obtain a type certificate from the responsible aviation regulatory authority. Since 2003, EASA is responsible for the certification of aircraft in the EU and for some European non-EU Countries. This certificate testifies that the type of aircraft meets the safety requirements set by the European Union.

(EASA: Aircraft certification)
Since February 2020 the UK is no longer a member state of EASA:

The United Kingdom withdrew from the European Union on 31/01/2020 at midnight (Brussels time) and is now a Third Country.

(EASA: United Kingdom)
Type certificates are therefore handled by the UK itself. The responsible authority is the CAA:

The CAA will issue a Type Certificate (TC) or Restricted Type Certificate (RTC) for the approval of Products (aircraft, engine or propeller) for UK applicants.

(CAA: Type certificates and restricted type certificates)
There is however a cooperation between EASA and the CAA as part of the EU-UK Trade and Cooperation Agreement:

On 24 December 2020, the EU and UK negotiators agreed on a Trade and Cooperation Agreement.
The Agreement applies from 1 January 2021.
Aviation Safety is covered by Part Two, Heading Two, Title II of the Agreement. The application of the agreement is currently limited to airworthiness and environment certification, covered by Annex 30 to the Agreement.

(EASA: EU-UK Trade and Cooperation Agreement)
When searching through the rather lengthy agreement (2564 pages), one finds:

Type certificates issued by the technical agent of the Union as certificating authority shall be
validated by the technical agent of the United Kingdom as validating authority. [...]
Type certificates issued by the technical agent of the United Kingdom as certificating
authority shall be validated by the technical agent of the Union as validating authority.

(Official Journal of the European Union, PDF, p. 1681 f.)
This means EU type certificates are not automatically valid in the UK, but will be validated by the CAA (therefore no new type certificate needs to be issued). This is similar to the agreement with the US or Canada:

EASA delivers the primary certification for European aircraft models which are also being validated in parallel by foreign authorities for operation in their airspaces, e.g. the FAA for the US or TCCA for Canada. Conversely, EASA will validate the FAA certification of US aircraft models (or TCCA certification of Canadian models) according to applicable Bilateral Aviation Safety Agreements between the EU and the concerned Third Country.

(EASA: Aircraft certification)
There is also a special Working Arrangement between EASA and the CAA regarding Rolls-Royce because of the German Rolls-Royce Deutschland subsidiary of Rolls-Royce plc, but this is for engine certification, not aircraft certification.


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How heavy and expensive are batteries and generators on a 737?
I am currently struggling to find details on generators and batteries. For a B737 or similar, what would the cost and weight (in £ and Kg) of a battery and IDG be? And do lightweight options exist or already used?

I just Googled "Boeing 737 Battery" and "Boeing 737 Generator" and a ton of useful looking links came up.  How hard have you looked?

I can't find an accurate value for the unit cost of these components. I can find stats but that is not what I need

Probably because they don’t sell them retail.

I know they don't sell them retail, that's why I'm asking here incase someone knows what they're worth.....

https://skygeek.com/saft-018550-000-nicad-battery.html. Likely you could negotiate a cheaper deal in bulk.


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Is it normal that an ELT activates during a strong up draft in flight?
I was flying a PA 28 181 Archer on a nice clear day at cruise speed level flight 3000ft. Suddenly, from nowhere it was hit by an up draft that lasted I would  say less than a second. I got pain in my back. Then I noticed that the led in the RCP of the ELT (Kannad 406 compact AF) was triggered.
Is this normal? Did anyone experienced anything like this?
Should I take the unit to the repair shop? It is only 3 years old.

ELTs are designed to be triggered by a high G force. It isn’t “normal” that this happens in the air, but in turbulence bad enough to cause you back pain, it’s not surprising. It’s more common with hard landings.

They aren't supposed to be sensitive to vertical accelerations at all (in helicopters, you have to mount the unit tilted down 45 degrees because helicopters need both vertical and horizontal sensitivity). However, a really hard gust could introduce some degree of longitudinal acceleration (possibly from the airplane's nose down response to the gust, or a mounting bracket that flexed slightly under the G load) so it's not unheard of.  Just remove the unit and do the normal shake test per the operating manual to confirm normal operation.

I think it's worth mentioning that if you experience enough Gs to trigger your ELT and injure yourself your aircraft could have been damaged. You should talk to an A&P about it.

Good point.  You just have to look at the wings for skin wrinkles. With metal structures, it's bent permanently if there are wrinkles, or it's not if there aren't and you are good to go.

I wouldn't agree with that @JohnK, it's not just structures, it could jar things loose in places.

Well, I was only referring to whether things like spars and ribs are bent or not.  It's a key difference from wood structures, were single-cycle overstress can leave cellular compression failures that go completely undetected unless the specific area can be inspected for the faint cross-grain telltales.

The manual for your ELT doesn't say exactly what triggers it (or I overlooked it) and the EUROCAE ED 62 standard is behind a paywall. The FAA ELT standard TSO C-126 isn't on the FAA site, possibly because it seems to be based on a commercial standard RTCA DO-204A, which is also behind a paywall.
However, your ELT complies with C-126 and I found a thesis called The sensitivity of aircraft emergency locator transmitters to nondistress impact events about false activation rates for ELTs that includes this (p.27):

TSO-C126 ELTs follow the specifications of RTCA DO-204, Minimum
Operational Performance Standards for 406 MHz Emergency Locator
Transmitters [15]. In these documents, the RTCA defined a crash as
when the longitudinal axis of the aircraft experienced a velocity
change of -3.5±0.5 feet per second (fps), with a minimum of
deceleration of 2±0.3 Gs.

If the turbulence you encountered exceeded those tolerances then I assume it would set off the ELT. I don't know if your unit needs repairs or a new battery, you would need to check with your repair shop. In the US there are required inspections and rules on when to replace batteries (14 CFR 91.207) but if your aircraft isn't a US one then that wouldn't apply to you.
I would get someone to look at your back before you worry about the ELT, though :-)


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What effect does towing a glider have on the stall speed of the tow plane?
I can see that if the tow is perfectly aligned with the axis of the engine thrust, that it is equivalent to pure parasitic drag and similar to some reduction of thrust. However, in the real world the tow is basically always misaligned to some degree or the other, with occasional significant yaw/pitch moments on the tail of the tow plane.

None
The effect of the glider is purely drag, which the tow plane must compensate for with more thrust.  Both aircraft lift themselves.  The tow plane thrust counteracts the induced and parasitic drag of the entire flying unit.
The effect on aerodynamic performance would be comparable to a twin with one engine out, or trying to fly with speed brakes open, with the added weight of the glider also affecting acceleration.  The weight issue is offset with the wings of the glider, so now you have a draggy biplane lifting more weight on only the towplanes thrust.
The tow plane, lifting only itself, will have the same stall speed (for its weight) theoretically, but ...
In practice, one may greatly increase safety margin by adding extra airspeed while taking off and climbing to help avoid the potentially disastrous effects of uncommanded changes in pitch, which could pull the tow plane over its stall AoA or nose it into the ground.
Proper location of the tow attachment on both aircraft would be useful in minimizing pitch tendencies, ie, close to the center of gravity, as well as careful piloting of the glider, and trimming of the towplane.

Actually, one might expect a glider to do very well lifting its weight with as little drag as possible.  Working on a 14,000 mile bipe 747 with a symmetrical variable AoA top wing as an extra fuel tank.

The dangerous problem is not so much stalling the tug as the glider doing too well lifting its own weight, getting higher than the tug, and pitching the tug nose down. This risk increases if the glider's "correct" position on a short tow rope is affected by the tug's downwash, and  a small upwards excursion quickly turns into a big one if it comes out of the downwash airstream. Turbulence can cause similar hazards.

@RobertDiGiovanni Assuming it's not in the wash of the plane.

On your last sentence, I presume you meant to refer to the centre-line of the aircraft, as attaching to the centre of gravity is (in practice) very bad.

@Mark Brockington why is it "bad"?  Any additional drag forces (not built into the towplane) could cause dangerous pitching torques.  Remember an aircraft has a CG on the vertical axis too.  Generally thrust and drag (from the glider too) will be somewhere near it.

Looking at this question from a fundamentals of flight perspective.  The airplane towing the glider would have its forces in balance as they usually would, however there is a glider in the back that is causing quite a bit of drag.
Since airplanes climb due to an excess of thrust, the airplane will climb at a much lower rate.  The pitch attitude would be lower during the climb to maintain the proper VY speed.  The pitch attitude at which the airplane stalls would be lower but under steady state flight (1G), the stall speed would remain the same.

Parts of your answer are not technically true.  Airplanes climb due to an excess of lift.  They can maintain that excess lift (and thus climb) if they can provide thrust to counteract the additional drag that that the lift provides (assuming that the parasitic drag doesn't change much whether climbing or in level flight).

I'm sorry.  You are incorrect.  An airplane climbs due to excess thrust.

@JonV -- see for example https://aviation.stackexchange.com/questions/40921/does-lift-equal-weight-in-a-climb/56476#56476, and other related answers to the same question. To a first approximation, in a steady climb, lift = weight * cosine (climb angle), and lift is therefore less than weight in a steady climb.

Yet at the same time, we can also observe that we need to have lift greater than weight to make the flight path curve from level up into a climbing path -- so if we could never generate more lift than weight, we could never climb -- and so the endless discussion goes on and on .  Anyway, for modest climb angles, the excess of  thrust compared to drag must be much greater than the discrepancy between lift and weight.  (At least, if we are speaking in terms of ratios.)

Well again, a glider would have zero effect on a stall speed of the tow plane, because the tow plane technically does not have a stall speed (remember wings only stall if they exceed the critical AoA - this can happen at any airspeed and/or at any flight attitude).
Now most tow planes use a release hook mounted under the fuselage just aft of the tailwheel.  That’s just about as close to the CL thrust axis of the aircraft as structure will allow.  If anything, this placement should tend to lower the nose of the tow plane and decrease its AOA.

If the glider is being towed in perfect alignment with the longitudinal axis of the tow plane and the thrust, then no - the stall speed will be the same.
In reality the tow would never be perfectly aligned like that and there would be some effect on the stall speed.
For instance, if the glider is low i.e. below the plane axis, there would be a downward component to the force acting on the tail of the tow plane, at the attachment point of the tow cable. This force is equivalent to an increase in weight (i.e increasing the stall speed) and a rearward shift of the C.G.
Nevertheless, during typical, stable tows, even a large 25m glider  generates no more than 40N or so of drag. Near the stall speed of a typical tow plane, that might drop to well under 15N. Even at a relatively very low tow, say 30 degrees below the plane axis, that means an equivalent of a mere 1.5lbs "weight" attached to the tail of the tow plane as far as the effect on the stall speed is concerned.
The opposite would apply for a high tow, i.e. a reduction of the stall speed.
Probably no effect by lateral shifts of the glider, assuming the tow plane remains coordinated.
Furthermore, as soon as the stall starts developing the tow plane's speed would start dropping resulting in a sharp decrease of the tension in the tow cable thereby practically eliminating any effect the tow might have had on the stall.
In short, the stall speed may increase or decrease depending on the glider's direction of deviation from perfect alignment with the plane axis, but the change is likely to be negligible in most real world conditions.

I'm not convinced a pull-up at the tail will lower the stall speed. This needs to be counteracted by extra negative lift of the horizontal stabilizer, and then to the main wing the situation looks the same. If it's not counteracted by the stabilizer, the tug will quickly pitch more and more steeply down – which certainly means it won't stall, but not that it can get any slower.


text:
Even if an intruder aircraft isn't equipped with TCAS, can I detect them with my TCAS?

I'm wondering about the TCAS operation concept.
If aircraft "A" is equipped with TCAS I or TCAS II equipment,
and aircraft "B" isn't equipped with either TCAS transponder or antenna,
then can aircraft "A" receive a "traffic adivsory" (TA) when aircraft "B" comes close?
When I check the 'FAA's introduction to TCAS' Table 1(6p),(see the picture)
if aircraft "A" is equipped with TCAS, then it always provides a "TA" in any situation.
Did I understand that correctly?

Aircraft "B" has to be equipped with at least a Mode A transponder for the TCAS in aircraft "A" to provide a Traffic Advisory to its pilot.
The way TCAS detects nearby aircraft is by interrogation their transponder. So if the other aircraft ("B") does not have any transponder (A, A/C, or S) then TCAS does not work.

If "B" is equipped "MODE S" but without TCAS unit and Antenna, "A" can detect the "B" by TCAS system?

@PARKMIN yes, if "B" has a functioning Mode-S transponder, the TCAS on "A" will detect "B" and provide both TAs and RAs.


text:
Is there any part of a flight where the pilot would pitch down?
Would the pilot ever pitch down (even slightly) during a flight, or would he/she simply reduce power to reduce altitude?
This question is not similar to Why do airplanes lift up their nose to climb? (asked by Chris) for it the reasons aircraft pitch up. This question is looking for an answer that explains if and when a pilot pitches down during a flight to reduce altitude, the very opposite of the question of @Chris.

possible duplicate of Why do airplanes lift up their nose to climb?

Could you be more specific of what you want to know? I could answer this in several ways and I am not sure which one would give you what you are looking for.

emergency descent (during decompression or TCAS warning) will have a pitch down.

@GdD, I was wondering whether the pilot would pitch down under normal circumstances. More specifically, from the beginning of the descent.

Fighter airplanes do regularly.

dive bombing comes to mind - but to avoid negative g loads, pilots would as well perform a half roll and pull. Gets you in a straight down direction equally well.

Aerobatic airplanes do it all the time.  It's the only way to do an outside loop.

Well if they pitch up to climb it's only logical that they would eventually pitch back down.

The most common case to pitch down is to speed up, not to reduce altitude, for example when transitioning from a climb (at climb speed) to level flight (accelerating to cruise speed). You can transition to level flight by reducing thrust, but that'll leave you level at climb speed, and is usually not what you want.
Changing configuration will usually require pitching changes to maintain stable flight. In particular during the approach-to-landing, extending the flaps will substantially increase the drag, and in order to maintain airspeed, you'll need to pitch the nose down. If you don't, you'll bleed off airspeed and potentially eventually stall unless you overpower the drag with thrust.
There are of course unusual circumstances that will require a pitch-down as well, obstacle avoidance for example (e.g. airplanes). As mentioned in the comments, to make a speedy descent you'll probably also want to pitch down (such as in case of pressurization problems or fire on board).

The reason you pitch down when deploying flaps is to counter the large increase in lift (the balloon). Every plane with flaps is capable of level dirty flight, otherwise a go-around, requiring a pitch up, would be impossible. When flying a constant AoA approach, the nose does control airspeed, but not because the engines can't maintain airspeed, but to keep the aircraft stable at a given AoA.

@RhinoDriver The increased lift comes with increased drag. You're effectively saying the same thing, but you subscribe to the 'pitch controls altitude' point of view. If you use power controls altitude and pitch controls airspeed, then your approach airspeed corresponds to a different pitch attitude with the new configuration. They're both valid and interconnected.
I also did not mention level flight, of course you can maintain level flight or even climb with flaps down. I'll remove the 'can' to make it less ambiguous

To add a bit of historical background, the argument used to rage as to whether you should "control altitude with pitch and speed with power" or "control altitude with power and speed with pitch." I always felt (and still do, though I'm long retired) that adhering to a hard line either way was a bit silly. Obviously you can use either to change either, within limitations of course. I don't know what current thinking is on the subject. In the end it's a matter of energy management.
There used to be at least one special case where you would want to change both altitude and speed by using pitch alone for a bit. On the 747-200 with certain engines, when starting a descent from high altitude (like the high 30s up to the max operating altitude), the recommendation was to start the descent by putting the nose down first and waiting until the airspeed started increasing before reducing power, thus avoiding the embarrassment of a possible high altitude flameout. My guess is that with modern engines and FADEC, this kind of thing is no longer an issue.

I'm going to interpret "normal" as cruise level of a commercial flight. Normal for other types of flying might have different answers.
In level flight pitch is regularly adjusted both up and down to maintain the  chosen altitude. Generally these adjustments are small enough that they are not noticed by passengers or crew, especially with an autopilot engaged. So is it very normal to pitch down in small increments without changing power settings.
With larger changes in pitch, for example when descending from cruise level, typically thrust is reduced or increased to maintain airspeed. It would be unusual to pitch down before reducing power, or pitch up before increasing it.

Descending from Class A airspace on approach to an airport, a commercial airliner will, in my experience, often pitch down slightly. It can be somewhat unnerving, especially as the engines will throttle down around the same time, but the nose-down is typically very shallow.
Whether a pilot continues to nose-down on final depends on the aircraft, the airport and the wind conditions. It's often a practical requirement to nose down at the runway in a high crosswind landing, in order to minimize the sideways slip produced by the crosswind as well as to traverse the layer of air containing the crosswind as quickly as possible.


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Why are there different types of winglets?
If all winglets serve the same purpose (to reduce vortex drag), why do different aircraft have different winglets? This question is not trying to get a comparison of the development of winglets/wingtips, with other aircraft components, as the question of @Manu H is.

@Federico, the questions do seem similar. However, they are addressing two different things.

Winglet design is driven more by marketing than by engineering, so every aircraft brand tries to cultivate their own, supposedly better, shape.
A study by Nita and Scholz (PDF!), Chapter 6 gives a good overview over recent winglet studies. A raked tip performs better, and if winglets could point downwards, they also could do better. As they are, they give only 28% to 38% drag reduction of an equivalent span increase.

Raked wingtip of the Boeing 777-300

Thanks! This is great. I take it the newer split winglets don't really include the benefits of a downward-pointing winglet, since they primarily point upwards?

@egid: A downward pointing winglet is only slightly better, and with the limited size cannot effect drag much. Theoretically, a variable-geometry winglet which can be folded up for landing would capture the benefit, but would work best when stopped halfway in the transition from pointing upward to pointing downward ;-)

@PeterKämpf Do you have link where you explain how raked wingtips works?Is raked wingtips better than simple horizontal extension?

@member2017 Yes


text:
Would adding a fairing to landing gear to spin the tires before landing yield enough benefits?
I was reading answers to this question: How long do airliner tires last? Can this be improved? and it seems to be reasonable to keep things simple and rethread tires instead of designing motors to spin them up.
However, what if one was to implement a simple aluminum housing like the one in the drawing below which will provide the following benefit.

When gear is deployed, due to friction of air only on the exposed part of tire thread, tire will spin up on it's own.

Has this ever been considered? Why would this kind of design work/not work for large airliners?
NOTE: the inside of the wheels are open for cooling purposes as well as various ducts can be incorporated for efficient cooling of the brakes.

"Has this ever been considered? " -> this type of wheel cover was common among aircraft with fixed undercarriage of the 1930's. Try: Fokker D.XXI, Fokker F.32, Junkers Ju 87, Mitsubishi A5M and many others. Seems to have disappeared with retracting undercarriage.

Yes, that makes sense when entire flight gear is deployed since it's fixed. What I mean is using similar approach to promote tire spin up.

This may interest you: US patent 6,032,900 http://www.google.com/patents/US6032900 (consider also previous patents cited in the text)

Research paper out of Embry-Riddle: http://commons.erau.edu/cgi/viewcontent.cgi?article=1043&context=ijaaa "The work performed in this study strongly suggests that a wheel spinup
device can improve the life of heavy aircraft main landing gear tires."

Check out this answer to a similar question. What it boils down to is that pre spinning gear has been looked into but there are implications of spinning up that kind of mass. The rotational inertia created created by doing so effects the handling of the aircraft. On a similar note its often easier to have a simple part that wears out and needs to be replaced often (like a tire) than a complex part that needs maintenance and is more likely to be problematic.
The part you describe is pretty common on small aircraft to reduce drag over the wheels. As far as I know it does not aid in spinning the tires. Since the tires are more or less flush the air simply flows over them.

For what its worth these boots also can get in the way. If the plane lands hard the tires will balloon out and rub up agains the sides of the boot (depending on the tolerances) this may break the boot the tire or both.

Got it, the gyroscopic force is the key :D

"boots" = wheel pants. Re: trade-offs related to "pre-spinning", I would suggest cost, weight, and reliability - all favour "let contact with the ground bring them up to speed".

For the spinning wheels due to airflow, this question may help.

My uncle told me the Air Force tried this in the 60's on some heavy aircraft but stopped testing for two reasons, first eventually someone would put them on backwards with obvious disastrous results, and secondly, an aircraft actually benefits from the initial braking impact that spinning the tires up gives it.
On smaller aircraft its helpful to get rid of that little bit of speed to help pilot transition from flight to "down and rolling". It reduces the aircrafts tendency to bounce back into the air. After a few thousand hours of flight time myself, I believe he was right.
Additionally, I have seen smaller tires (tailwheels) spinning in flight on some aircraft as air sped past their bottom surfaces, I have not seen this tendency on main gear(faired or not).

This was tried in the '50s by providing small flaps on the tires which caught the air and spun the tire prior to touchdown.  Medium and mixed success.  Don't know why it never caught on.

You may add references to improve your answer. Doing so increases your answer's quality and provides further readings and a set of links for those wanting to know more.

Given that the question is asking why such a system never caught on, an answer saying that you don't know is unlikely to be considered useful.


text:
Why is a model quadcopter 'better' than a helicopter? Why doesn't this scale up to the full-size versions?

EDIT
Soon after I posted this, it was pointed out that a similar question
  exists. That other question answers most of mine. I shall leave this here as a stub. That way it provides a pointer to the other question and, importantly, my title contains all the keywords 'model', 'quadcopter','helicopter' and 'scale up' whereas the other question's title (Why haven't quadcopters been scaled up yet?) is less comprehensive and therefore less searchable.

Model helicopters were on the market for many, many years before quadcopters.
Presumably most of the engineering bugs had been removed by then as well as control issues.
Suddenly along comes the new kid on the block and it's all change.
Related questions

Why are model quadcopters so popular in relation to model helicopters?
How come the same reasons don't apply to full-size helicopters and quadcopters? Why don't we see search and rescue quadcopters and personnel-carrying quadcopters?

At least the second question is answered here

@PeterKämpf Hmm - yes. That is very similar. I'll read that one and see if it answers my question. Then I'll decide whether to edit/delete mine or not. Thanks.

Quadcopters have brought a whole new world to the new Rc market. I have one and a rc helicopter and like the quadcopter more. My Dad said that he loved the way it manuveured, and that might be why they are more popular because they can perform manuveurs that an RC helicopter cannot. RC helicopters don't have good range and don't fly very well, but with certain quadcopters you can fly it up to 5,000ft in the air and most of them have an attached camera so you can get incredible views. Also honestly the quadcopter is better looking than the rc helicopter, it looks more stealthy.

That's interesting about the range. I don't think that was covered in the other question. I wonder why the range should be so different.

Cheap MEMS gyroscopes have been on the market only since maybe 10 years. Before you needed more bulky and expensive gyros. Also, cheap and powerful micro controllers which can process the sensor data quickly enough and can control the speeds of the four motors to stabilize the quadcopter have only been available recently. The third recent innovation was more gradual, but also the storage density of batteries was not available maybe 20 years ago. With modern LiPo batteries you can have flying times of several minutes where NiCd batteries only gave you a fraction of that time for the same mass.
For your second question: The reason is similar to why birds have not been scaled up to carry humans, like horses do. This answer should give a good explanation.


text:
Can I log CO-Pilot and Multi-Pilot hours as a safety pilot?
I am working for a UK airline as a First Officer. I have in my roster some flights where I am acting as safety pilot for FO's conducting line training. I am wondering if I can log my hours as CO-Pilot and Multi-Pilot time as well as include it in my Total time. I am UKCAA licensed so regulations from the UK authority on this would be greatly appreciated.

Please describe who is sitting in what seats & who is doing what specific duties during the time that you are "acting as safety pilot for FO's conducting line training."

I am an FO acting as safety pilot for the flight sitting in the Jump seat. Captain is still there as PIC and FO in the right hand seat on line training flights. My primary role is to ensure no called or actions are missed and assist with anything where the work load get to high for the training FO

As far as I know, I think I can still log it as co-pilot + multi-pilot as I am a required member of the crew as the 'FO' has not been signed off yet


text:
Can I legally own and fly fighter jets in the UK?
I’ve seen a similar post, but it applied to America. Could I own and fly a BAE Systems Hawk T1 in the UK? What kind of regulations are there? Obviously it would have to be unweaponised but I was just wondering about the specifics.

I don't know of any privately owned Hawks, but there are many ex-RAF jets in private ownership, like the Jet Provost, Lightning, Gnat, Meteor, Vampire, and others I can't remember. The Ministry of Defence sells fixed-wing airplanes and helicopters occasionally at auction; when they retire the Hawk T1 you could be able to pick one up.
This CAA document goes over many of the particulars, a quick summary is that in almost all cases they would be under a permit to fly. This would require an inspection to clear it for the permit, and an (un)healthy dose of paperwork. I know of no way to get these aircraft certified, but you can get them cleared for night and IFR flight with extra paperwork and continued inspections, provided the aircraft is equipped for it. You can also get a permit to fly faster than 250kt below 10,000ft, which in a jet like the Hawk would be an advantage. Flying abroad on a UK permit aircraft is just more paperwork: you have to get permission from all the countries you'd fly over and land at, which is generally a formality, and restricted to day VFR.
One of the challenges you would find is keeping the plane airworthy. There are a few organizations that restore and maintain ex-military jets; you'd want to find out if they'd be able and willing to take it on for you before you buy it.
Of course you'd also need an awful lot of money. Jet Provosts (50s era trainers) are at the low end of jets as costs go and they still cost £600 per hour to operate!

Comments are not for extended discussion; this conversation has been moved to chat.


text:
Logo light source placement on CRJ 900
I understand that for most commercial aircraft, the source of the logo lights originates from the horizontal stabilizer which is projected onto the vertical stabilizer. However, I don't see how this could work for the CRJ 900 or other aircraft with a T-tail configuration. Can these aircraft also have logo lights, and if so where would the light originate from?

Surely a light can shine down from the horizontal stabilizer to the vertical stabilizer?

The Bombardier CRJ series has the logo lights installed on the engine pylons:

E. Logo Lighting
A white logo light is installed on the upper surface of each engine pylon to illuminate the
airline logo on each side of the vertical stabilizer. The lights are controlled by a LOGO
switch on the EXTERNAL LTS panel.

(Bobmardier CRJ-700/-900 FCOM - Lighting)
Some other aircraft with a T-tail have the logo lights installed on the lower surface of the horizontal stabilizer, e.g. the Dash-8 Q400:

12.14.5.8 Logo Lights
White logo lights are installed flush with the bottom left and right horizontal stabilizers. The logo
lights supply lighting for the logo on the vertical stabilizer.

(Bombardier Dash-8 Q400 FCOM - Lighting System)

on 737s (at least the older ones) the logo light is out on the wingtip.

@Anilv That's weird, never heard of that before. Newer ones have them on the horizontal stabilizer. But the 737 is not a T-tail of course.

This link shows how some 737 classics had logo lights installed on the wingtips, although it was an option & plenty of classics didn't have them. All NG & Max 737s, AFAIK, have logo lights, which are on the horizontal stab.

And this photo shows what the light on the wintip itself looked like on those Classics which had them.


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What is the purpose of this box behind the yoke on a 737?
I was looking at the 737 cockpit when I found this apparatus behind the yoke. I have never seen it before and I have no idea what is does. Can anyone help me?

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.

Do you mean the yellowish handle?

Why the close vote?